AD remains incurable despite recent advances suggesting therapeutic targets. This proposal will investigate RNA interference (RNAi) as a novel therapeutic approach to suppress genes central to the disease process in AD. Studies of familial AD have revealed the critical role of beta-amyloid (A-beta) production in AD pathogenesis. Both the parent protein of A-beta, amyloid precursor protein (APP), and the APP-cleaving enzyme beta-secretase, BACE1, are attractive RNAi targets in AD because they are required for A-beta production yet are not essential in mice. Building on our recent success in suppressing these two genes in vitro, we will use viral-mediated RNAi to suppress APP and BACE1 in AD mice that are transgenic for the well-studied Swedish mutation of APP (APPsw). The central hypothesis is that RNAi will prove to be an effective and selective strategy to slow, and perhaps reverse, pathogenic processes in AD. Aim 1 will test the ability of short hairpin RNA (shRNA)-expressing virus to suppress APPsw expression and A-beta accumulation in cultured neurons and the hippocampus and cortex of AD mice. Viral delivery to mice will determine whether RNAi can prevent or reverse amyloid deposition, plaque formation and other pathological hallmarks of AD. Similar studies in aim 2 will test whether viral delivery of BACE1 shRNA effectively suppresses endogenous BACE1 expression, Ab-beta production and plaque formation. Viral delivery before and after A-beta deposition in transgenic mice will address whether pathological changes can be prevented or reversed by BACE1 suppression. Because APP and BACE1 are divergent targets with distinct biological activities, the benefits and possible adverse outcomes of suppressing either gene in the context of ongoing AD pathology may differ. Thus, aim 3 will directly compare these two suppression strategies to each other and to suppression by a novel dual-shRNA virus that targets both APPsw and BACE1.